diff --git a/.github/workflows/linux.yml b/.github/workflows/linux.yml
index d1de9a7..cc83baf 100644
--- a/.github/workflows/linux.yml
+++ b/.github/workflows/linux.yml
@@ -14,7 +14,7 @@ jobs:
     steps:
     - uses: actions/checkout@v2
     - name: Install dependencies
-      run: dnf install -yq cmake ninja-build clang-tools-extra python3-PyYAML
+      run: dnf install -yq cmake ninja-build gcc-c++ clang-tools-extra python3-PyYAML
 
     - name: Build with GCC
       run: |
diff --git a/poly2tri/common/shapes.cc b/poly2tri/common/shapes.cc
index c044311..6e65dc6 100644
--- a/poly2tri/common/shapes.cc
+++ b/poly2tri/common/shapes.cc
@@ -352,12 +352,18 @@ void Triangle::SetDelunayEdgeCW(const Point& p, bool e)
 // The neighbor across to given point
 Triangle& Triangle::NeighborAcross(const Point& opoint)
 {
+  Triangle* neighbor = nullptr;
   if (&opoint == points_[0]) {
-    return *neighbors_[0];
+    neighbor = neighbors_[0];
   } else if (&opoint == points_[1]) {
-    return *neighbors_[1];
+    neighbor = neighbors_[1];
+  } else {
+    neighbor = neighbors_[2];
   }
-  return *neighbors_[2];
+  if (neighbor == nullptr) {
+      throw std::runtime_error("NeighborAcross - null neighbor");
+  }
+  return *neighbor;
 }
 
 void Triangle::DebugPrint()
diff --git a/poly2tri/sweep/sweep.cc b/poly2tri/sweep/sweep.cc
index cac7e69..1f51fee 100644
--- a/poly2tri/sweep/sweep.cc
+++ b/poly2tri/sweep/sweep.cc
@@ -54,8 +54,8 @@ void Sweep::SweepPoints(SweepContext& tcx)
   for (size_t i = 1; i < tcx.point_count(); i++) {
     Point& point = *tcx.GetPoint(i);
     Node* node = &PointEvent(tcx, point);
-    for (unsigned int i = 0; i < point.edge_list.size(); i++) {
-      EdgeEvent(tcx, point.edge_list[i], node);
+    for (unsigned int j = 0; j < point.edge_list.size(); j++) {
+      EdgeEvent(tcx, point.edge_list[j], node);
     }
   }
 }
@@ -123,8 +123,7 @@ void Sweep::EdgeEvent(SweepContext& tcx, Point& ep, Point& eq, Triangle* triangl
       triangle = &triangle->NeighborAcross(point);
       EdgeEvent( tcx, ep, *p1, triangle, *p1 );
     } else {
-      std::runtime_error("EdgeEvent - collinear points not supported");
-      assert(0);
+      throw std::runtime_error("EdgeEvent - collinear points not supported");
     }
     return;
   }
@@ -140,8 +139,7 @@ void Sweep::EdgeEvent(SweepContext& tcx, Point& ep, Point& eq, Triangle* triangl
       triangle = &triangle->NeighborAcross(point);
       EdgeEvent( tcx, ep, *p2, triangle, *p2 );
     } else {
-      std::runtime_error("EdgeEvent - collinear points not supported");
-      assert(0);
+      throw std::runtime_error("EdgeEvent - collinear points not supported");
     }
     return;
   }
diff --git a/testbed/data/deadly_quad.dat b/testbed/data/deadly_quad.dat
new file mode 100644
index 0000000..7e4b217
--- /dev/null
+++ b/testbed/data/deadly_quad.dat
@@ -0,0 +1,4 @@
+0.0     0.0
+1.0e-05 0.0
+1.1e-04 3.0e-07
+1.0e-04 3.0e-07
diff --git a/unittest/main.cpp b/unittest/main.cpp
index 6978b33..671b216 100644
--- a/unittest/main.cpp
+++ b/unittest/main.cpp
@@ -5,6 +5,7 @@
 #include <fstream>
 #include <iostream>
 #include <iterator>
+#include <stdexcept>
 
 BOOST_AUTO_TEST_CASE(BasicTest)
 {
@@ -40,6 +41,22 @@ BOOST_AUTO_TEST_CASE(QuadTest)
   }
 }
 
+BOOST_AUTO_TEST_CASE(QuadTestThrow)
+{
+  // Very narrow quad that demonstrates a failure case during triangulation
+  std::vector<p2t::Point*> polyline {
+    new p2t::Point(0.0,     0.0),
+    new p2t::Point(1.0e-05, 0.0),
+    new p2t::Point(1.1e-04, 3.0e-07),
+    new p2t::Point(1.0e-04, 3.0e-07)
+  };
+  p2t::CDT cdt{ polyline };
+  BOOST_CHECK_THROW(cdt.Triangulate(), std::runtime_error);
+  for (const auto p : polyline) {
+    delete p;
+  }
+}
+
 BOOST_AUTO_TEST_CASE(TestbedFilesTest)
 {
   for (const auto& filename : { "custom.dat", "diamond.dat", "star.dat", "test.dat" }) {